In hard disk drives, data is written to and read from magnetic recording media, herein called disks, utilizing magnetoresistive (MR) transducers commonly referred to as MR heads. Typically, one or more disks having a thin film of magnetic material coated thereon are rotatably mounted on a spindle. An MR head mounted on an actuator arm is positioned in close proximity to the disk surface to write data to and read data from the disk surface.
During operation of the disk drive, the actuator arm moves the MR head to the desired radial position on the surface of the rotating disk where the MR head electromagnetically writes data to the disk and senses magnetic field signal changes to read data from the disk. Usually, the MR head is integrally mounted in a carrier or support referred to as a slider. The slider generally serves to mechanically support the MR head and any electrical connections between the MR head and the disk drive. The slider is aerodynamically shaped, which allows it to fly over and maintain a uniform distance from the surface of the rotating disk.
Typically, an MR head includes an MR read element to read recorded data from the disk and an inductive write element to write the data to the disk. The read element includes a thin layer of magnetoresistive sensor stripe sandwiched between two magnetic shields that are electrically connected together but are otherwise isolated. The shields are constructed so that one is just upstream of the sensor stripe and one is just downstream of the sensor stripe. A constant current is passed through the sensor stripe, and the resistance of the magnetoresistive stripe varies in response to a previously recorded magnetic pattern on the disk. In this way, a corresponding varying voltage is detected across the sensor stripe. The magnetic shields help the sensor stripe to focus on a narrow region of the magnetic medium, hence improving the spatial resolution of the read head.
Earlier MR sensors operated on the basis of the anisotropic magnetoresistive (AMR) effect in which a component of the read element resistance varied as the square of the cosine of the angle between the magnetization and the direction of sense current flowing through the read element. In this manner, because the magnetic field of the recording media would effect the magnetization direction within the read element, the change in resistance could be monitored to determine the type of external magnetic field applied by the magnetic recording medium. Most current disk drive products utilize a different, more pronounced magnetoresistive effect known as the GMR or spin valve effect. This effect utilizes a layered magnetic sensor that also has a change in resistance based on the application of an external magnetic field. While multiple layers are typically used, the most relevant layers are a pair of ferromagnetic layers separated by an electrically conductive non-magnetic spacer layer such as copper. One of the ferromagnetic layers known as the “free” layer is a soft magnetic material whose magnetization is changed by the external magnetic field caused by the close proximity of the magnetic recording medium. The other ferromagnetic layer, known as the “pinned” layer, is also a soft magnetic material that has its magnetization direction fixed by an adjacent layer known as the “pinning” layer. A layer of antiferromagnetic material is typically used as the pinning layer. A sense current is passed from one end of the ferromagnetic and conductive layers to the opposite end of those same layers. The resistance of this tri-layer structure is proportional to the cosine of the magnetization angle between the two ferromagnetic layers. Since one of the layers has a magnetization angle that is pinned and the other ferromagnetic layer has a magnetization that can vary in response to the magnetic field from an adjacent magnetic recording medium, the resistance of the tri-layer structure is a function of that magnetic field from the recording medium. It has been discovered that this tri-layer structure behaves in this manner because of a spin dependent scattering of electrons, the scattering being dependent on the spin of the electron and the magnetization direction of the layer through which the electron passes.
Typically, MR sensors have not included shields at either end of the sensor stripe in what is known as the cross track direction. Various recent advances in commercial MR sensors, however, have increased the need for cross-track shielding. Competitive pressures within the computer industry require progressively increasing storage capacity within a given footprint for a disk drive. To provide this increased storage capacity, it is necessary to increase the areal density of data stored on the magnetic media. The data is stored in bits on linear tracks. The number of bits per inch in each track and the number of side-by-side tracks per inch are two parameters that determine the areal density. Another parameter is the bit aspect ratio (BAR), which is the ratio of the width (cross-track dimension) of an individual bit to the length (down-track dimension) of an individual bit. While commercial disk drive systems have typically had a BAR of approximately 20, the need for increased areal density has driven the BAR of more current disk drives down to approximately 7. Because of this shrinking of the BAR, the effect of adjacent tracks on the read process is becoming more pronounced.
It also aids in understanding to appreciate that the widths of the top and bottom shields are very great compared to the width of the MR sensor stripe. While the sensor stripe is approximately of the same width as a track, the shields are orders of magnitude wider. This is shown in FIG. 2 in which a first track 100 of bits 106 is adjacent to a second track 102 of bits 106, which in turn is adjacent to a third track 104 of bits 106. A read head 108 having an MR sensor stripe 110 is centered over the second track 102. It can be seen that the sensor stripe 110 is of approximately the same width as the bits 106 of each track.
In addition, the gap between the top and bottom shields, since it is selected to be proportional to the length of the bit, has increased relative to the width of the MR sensor stripe. Further, in actuality the top shield does not have a bottom surface that is parallel to the top surface of the bottom shield. This is because the top shield is deposited on top of the sensor stripe and on top of the permanent magnets and conductors/leads on either side of the sensor stripe. Since the permanent magnets and conductors/leads on either side of the sensor stripe are taller than the sensor stripe itself, the portion of the top shield above the sensor stripe is closer to the bottom shield than are the portions of the top shield above the permanent magnets and conductors/leads on either side thereof. It may be that the off-track gap is as much as twice the on-track gap. For this reason, the gap spacing is larger in regions offset in the cross-direction than it is directly over the track intended to be read.
U.S. Pat. No. 6,466,419 (Mao) discloses an MR sensor with side shields. A “current perpendicular to plane” (CPP) spin valve head is disclosed in which side shields exist to partially enclose the sensor stripe in the cross-track direction. Unfortunately, there is little to no discussion in Mao of how to manufacture such a structure. Further, there is no discussion of how to implement side shields in structures that are biased in any manner other than pile biasing of a CPP sensor.
It is against this background and a desire to improve on the prior art that the present invention has been developed.